How can I specify condition to derive account for SLA Acocunting rule?

Summary:

I need to derive an account based on the condition of the first 3 chanracters of Item Number.
This is for WIP Compmetion Return trasaction type of Costing.
I am not sure where the generic expression can be specified for Item Number like ****%.

Do I have to define an user function derive the first 3 charachers of the item first, then specify the function in the condition of Accouting Rule?

Any information is so welcome.

Content (please ensure you mask any confidential information):

Sated in the above.

Version (include the version you are using, if applicable):

24D, Costing of SCM

Code Snippet (add any code snippets that support your topic, if applicable):